(1) Field of the Invention
This invention relates to a vapor process for mineral dyeing cellulosic textile fabrics.
(2) Description of the Prior Art
Green mineral dyeing of cellulosics has been accomplished in prior art processes designated as "pearl gray" finishing. Heretofore, soluble chromium compounds, principally chromic chloride, were padded on cellulosics, dried and then converted to hydrated chromium oxide when wetted with an alkali hydroxide or carbonate solution. This is followed by heat curing to produce insoluble greenish chromium oxide deposit in the cellulosic achieving "mineral dyeing". Such treated fabrics have many uses and applications for items which are subjected to humid or outdoor environments such as tents, awnings, tarpaulins, beach fabric, curtains, boat and marine covers, etc.
Mineral dyeing is applied by double decomposition techniques wherein several baths and washings are required, or by treatment with a "single bath" obtained by mixing a higher valent Cr(VI) solution with a reducing chemical solution that results in developing the insoluble greenish chromium (III) oxide to "mineral dye" the cellulosic fabric. The double decomposition process requires at least two paddings of the fabric with separate treatment baths, drying or heat treatments, and a final washing and drying. Effluents from treatment and washing baths contain appreciable amounts of chromium (III). Problems arise in preventing environmental pollution from disposing of such waste materials. The referred to "single bath" process of the prior art avoids some of these just mentioned problems. This treatment bath, prepared by mixing the chromium solution and reducing solution, has limited useful life, being stable as a padding mixture for usually just about a day or so after mixing.